1. Field of the Invention
The present invention relates to an electrophotographic image forming apparatus.
2. Description of the Related Art
Electrophotographic image forming apparatuses can form high-quality images with simple operations in a short time, and they are also easy to maintain and manage. For these reasons, electrophotographic image forming apparatuses are in widespread use as, for example, photocopiers, printers, and facsimile machines. An electrophotographic image forming apparatus (hereinafter simply referred to as an “image forming apparatus”) has, for example, a photoreceptor, an electrostatic charging section, an exposure section, a developing section, a transfer section, and a fixing section. The photoreceptor is a roller-like member having a surface on which a photosensitive film is formed. The electrostatic charging section is energized with voltage and thereby charges the photoreceptor surface to a predetermined potential. The exposure section irradiates the charged photoreceptor surface with signal light according to image information to form an electrostatic latent image. The developing section feeds a toner to the electrostatic latent image to develop a toner image on the photoreceptor surface. The transfer section transfers the toner image on the photoreceptor surface to a recording medium. The fixing section includes, for example, a fixing roller that has a heating part therein, and a pressure roller that is in pressure contact with the fixing roller. The recording medium that carries the un-fixed toner image passes through the pressure-contact portion of the fixing roller and the pressure roller, whereby the toner image is thermally fixed to the recording medium. An image is thus printed on the recording medium.
The developing section has a developing roller opposed to the photoreceptor which rotates with an electrostatic latent image formed thereon, and a developing tank containing a developer. In the developing section, the developer in the developing tank is conveyed by the developing roller toward the photoreceptor, thereby developing the electrostatic latent image on the photoreceptor. Here, in the case where the developer is a two-component developer containing a toner and a carrier, only the toner is used for the development and consumed while the carrier is left in the developing tank. A new toner is replenished into the developing tank by a toner replenishment unit in an amount corresponding to the amount of the consumed toner.
In the case where a two-component developer containing a carrier and a toner for the developing section, it is necessary to mix and agitate the carrier and the toner by an agitating member. The agitating member first performs what is called a preliminary agitation, in which the developer in the developing tank is agitated for a certain time to be electrostatically charged to a predetermined value or higher, before the developing section performs a developing operation. Then, when the developing section starts the developing operation, the developer is fed to the photoreceptor while the developer in the tank is agitated or while the toner replenished from a toner cartridge and the developer in the tank are mixed and agitated. The developer fed to the photoreceptor is used for development of the electrostatic latent image.
The toner replenishment from the toner cartridge to the developing tank is carried out as follows; a feed port on the cartridge side and a replenishment port on the developing tank side are allowed to communicate with each other, and an appropriate amount of a toner is replenished from the cartridge to the developing tank according to predetermined timing.
The feed port on the cartridge side and the replenishment port on the developing tank side are each provided with a shutter, and each shutter opens when replenishing the toner or when the positions of the toner cartridge and the developing tank are fixed in such a state that the toner does not leak out. In addition, the shutter is closed at least when the toner cartridge and the developing tank are detached from each other, so that the toner does not leak out from the feed port and the replenishment port.
In an image forming apparatus disclosed in Japanese Unexamined Patent Publication JP-A 2007-78848, a toner is replenished through a toner conveyance pipe disposed between a toner hopper and a developing tank, and the feed port of the toner conveyance pipe is opened and closed according to a movement of a lever member upon attachment and detachment of a developing device.
A problem with the conventional structure is that a toner leaks out or scatters due to vibration caused by the operation of attaching and detaching the developing device since the shutter opens and closes in conjunction with the attachment and detachment of the developing device.
Further, in a color image forming apparatus, it is common to use developing devices for respective toners of four colors and therefore, in the case where toner containers are located in upper parts of the developing devices, it is difficult to install the developing devices from an upper part of the color image forming apparatus, thus causing a problem that there is no other way but to install the developing devices in an apparatus main unit through a front side thereof.